1. Field of the Invention
The present invention relates to an instrumentation control system in which attached information is transferred between control devices which are connected to a network and operate asynchronously.
2. Description of the Background Art
In general, in some of the various plants, a measurement control system is adopted in which a control device is provided in each of facilities, various control arithmetic processings are performed based on data measured by a measurement equipment to control each of the facilities, the arithmetic results thereof are transferred to a control device on the center side through a network, the control device on the center side monitors the state of the facilities of whole plant based on the arithmetic results, and the results of monitoring thereof are transferred to the control device of each of the facilities so that each of the facilities is feedback-controlled.
Besides, a dispersed processing system is also adopted in which plural control devices are provided in parallel for each of facilities, the respective control devices are connected to each other through a network, and the control of each of the facilities is shared by the plural control devices.
In the system as stated above, transfers of data are frequently performed asynchronously between the control devices in such a way that data obtained by the control arithmetic processing performed by one control device is transmitted to another control device, and another control device executes a specified control arithmetic operation based on the data, and transmits the arithmetic result thereof to next control device.
Here, when an abnormal transition phenomenon (for example, excessive change of pressure, flow rate, or temperature) occurs in each facility of the plant, the data measured by the measurement equipment is not reliable, and accordingly, the arithmetic result of the control device based on the measurement data is also not reliable.
The arithmetic data as stated above is transmitted to another control device, and when another control device performs an arithmetic operation based on the unreliable arithmetic data, the next arithmetic processing result also becomes unreliable.
In the case where the operation result becomes unreliable due to the abnormal transition phenomenon as stated above, when the arithmetic processing data is transmitted to another control device, as shown in FIG. 2, each control device adds unreliable information (for example, an unreliability flag “1”) to notify that the control operation result of each control device using this unreliable data is also unreliable, and mutual attentions are exchanged.
In the related art, a plant diagnosis method is proposed in which when an abnormal transition phenomenon occurs in each facility of a plant, an observation signal of the starting point of the transition change and a passage of the transition change in the observation signal are estimated, cause candidates are narrowed, and support is performed so that the cause of occurrence of unreliability can be quickly removed (see, for example, patent document 1).
[Patent document 1] Japanese Patent No. 2896306
In the related art disclosed in patent document 1, the cause of the occurrence of the unreliability such as the abnormal transition phenomenon is diagnosed and the countermeasures can be quickly taken. However, there is a problem that the unreliable informations are kept continuously transmitted among the control devices even after the causes of the unreliability are substantially removed.
That is, as a simple model, for example, when a closed loop of feedback control or the like is formed between two control devices A and B, even if the abnormal transition phenomenon to cause the unreliability is already removed in the control device A, since the unreliable information is added to data which was transmitted from the device A to the device B before that, data subjected to arithmetic processing in the device B based on this data becomes unreliable.
Accordingly, unreliable information is added also to the data fed back from the device B to the device A.
Further, unreliable information is added also to the result of arithmetic processing in the device A.
As stated above, there occurs a disadvantage that when the unreliable information is once added, the unreliable information is kept continuously transmitted between the control devices A and B.
When synchronous transmission is performed between control devices, it is relatively easy to cause reset timings of unreliable information to coincide with each other. However, when it is assumed that asynchronous transmission is performed between control devices, it is not simple to reset the unreliable information remaining in the closed loop.
As a countermeasure for removing the disadvantage as stated above, it is conceivable that a reset switch to reset the unreliable information is provided for each control device, and all reset switches are depressed at the same timing in the respective control devices to reset the unreliable information remaining in the closed loop between the devices.
When two control devices are adjacently disposed, it is possible to depress the reset switches at the same time. However, since the respective control devices are generally installed at places apart from each other through a network, even if operators communicate with each other, it is difficult to cause the timings of depressing the reset switches to coincide with each other completely. Accordingly, it is very difficult to reset the unreliable information remaining in the closed loop.
Besides, even in the case of taking a countermeasure to stop transmission of unreliable information unconditionally at the loop inlet so that the unreliable information is not transmitted in a closed loop formed between control devices, because of differences in application change timings of the respective devices or reconstruction timings, it is difficult to ensure an opportunity to extract a portion forming the closed loop after data of all devices are inputted.